[TUT] Handling - Acceleration Editing

NOTE: This tutorial is a re-formatted version of my GTASA Handling: Acceleration tutorial and the web page will be updated from the discussions in this thread. There have been a lot of topics on the forums on this subject, so hopefully having this guide will make forum searches bring up the information people are looking for rather than having to hope Project Cerbera appears from a Google search.

(Hopefully the topic title and description match whatever the current forum convention is, since the Tutorial Presentation thread was never updated from the obsolete format.)


GTASA Handling: Acceleration
Acceleration in GTASA works differently to previous editions. My tutorials about acceleration and detailed acceleration in GTA3 and GTAVC show a very different system to GTASA.

The relevent values in GTASA handling.cfg work like this:-

• Top Speed does not change anything unless you enable the USE_MAXSPD_LIMIT flag in the HandlingFlags setting.
  
• Drag Multiplier does change acceleration.
  
• Drag Multiplier does change top speed.
  
• Mass does change acceleration.
  
• Mass does not change top speed.
  
• Engine Inertia does change acceleration.
  
• Engine Inertia does not change top speed.
  
• Acceleration does change acceleration.
  
• Acceleration does change top speed.
  

There are some interesting features of the gameplay as well:-

• Driving up hills does reduce top speed.
  
• Driving down hills does not increase top speed.
  
• Driving up or down hills does change the rate of acceleration.
  
• Leaning forward slightly on motorbikes does increase top speed.
  
• Retracting the landing gear of planes does increase top speed.
  
• The maximum possible speed of vehicles in the game seems to be 287km/h which is about 178mph.
  

Flying vehicles have special data in the handling.cfg file where you can set how much the drag is reduced by retracting the landing gear. The effect of special data on acceleration is not covered in this tutorial.

Preparing for Experiments
All the experiments on this page are based on a completely original "Taxi" handling line. The "Taxi" is the modern yellow one - not the old "Cabbie" car. The original handling for the Taxi is:

CODE

TAXI 1450.0 4056.4 2.2 0.0 0.3 -0.25 75 0.80 0.75 0.45 5 180.0 19.0 10.0 F P 9.1 0.60 0 35.0 1.4 0.1 0.0 0.25 -0.15 0.54 0.0 0.2 0.51 20000 0 200000 0 1 0

Effect of Engine Acceleration on Top Speed

More acceleration means a higher top speed, as you would expect. However, there is an artificial limit to the maximum speed a vehicle can reach. This is partly based on the Drag Multiplier, which is tested next.

Effect of Drag Multiplier on Top Speed

With a value of "0" for Drag Multiplier the Taxi reached a top speed of 214km/h but with no drag, the car should just keep getting faster and faster. Obviously the game is preventing the car from going as fast as it should do. Using a value of "1.0" for Drag Multiplier gives the same value as "0" so it seems values below "1.0" are assumed to be "1.0" to prevent high speeds being reached.

With a large Acceleration value and a low Drag Multiplier, it might be possible for cars to reach the 270km/h limit which planes have.


Normal Taxi Acceleration Curve

Now the experiments go from top speed to the way the car accelerates. By comparing this curve of the standard Taxi acceleration to the graphs below, you can see the different effects of different parameters.

Effect of Engine Inertia on Taxi Top Speed

This seems to be the key value to better acceleration curves. A higher Engine Inertia value will make acceleration more gradual without lowering the top speed. Unfortunately, the limited top speed makes the car suddenly stop accelerating when it should gradually stop accelerating.

Effect of Drag Multiplier on Taxi Acceleration Curve

We have already seen the effect of Drag Multiplier on top speed, so here we see how it effects the way the car accelerates. Basically, a high drag makes the vehicle accelerate more slowly and reach a lower top speed. Interestingly, a low Drag Multiplier means the car takes longer to reach its top speed, which is increased. Another important part of realistic acceleration.

Effect of HandlingFlag Boosts on Taxi Acceleration Curve
I have not experimented with this yet.


Realistic Acceleration?
Perfectly realistic acceleration is not possible in GTASA but it is possible to get a semi-simulation style of acceleration. It can be made better than I my GTA3 Handling Overhaul and the more recent GTAVC Handling Overhaul did it, too.

To make acceleration more real:-

• Enable the USE_MAXSPD_LIMIT flag so that the special acceleration mode is used.
  
• Use a Drag Multiplier value of "1.0" to get higher top speeds since the original setups all have very low top speeds.
  
• Use a much higher EngineInertia value to make acceleration more gradual. Most of the original setups reach top speed far too quickly.
  
• Use roughly the same Engine Acceleration. This is so the acceleration force matches the available grip.
  
• Use a lower Braking Force.
  

Since slowing down is just negative acceleration, it deserves attention. Nearly all the original setups will cause the wheels to stop moving when you use the brakes, which makes the car impossible to turn. I set the braking force lower, so the wheels can just about keep moving when you use the brakes. This allows you to turn a little while braking, giving more realistic control over how you enter each corner.


(EDIT) Acceleration of 100.0 and Drag Multiplier value of 1.0:

800 x 600 - kB.

This seems to be the maximum speed which a car can reach without enabling the USE_MAXSPD_LIMIT flag.

When the USE_MAXSP_LIMIT option of the HandlingFlags value is set, the vehicle's acceleration curve will be stretched to try and reach the Top Speed setting. However, if there is not enough acceleration then the vehicle will never actually reach the Top Speed limit. Setting the acceleration so that the car gets close to the limit without reaching it enables realistic acceleration. You need a very high Engine Inertia (about 100!) to keep the acceleration rate sensible.

The result is acceleration a bit like you get in Gran Turismo. I am currently working on custom handling for the Infernus and Turismo using this new technique.